Plato, Selves and Composition

On the traditional dualist account of human beings, they are composed of essentially two parts, a body and a soul, but the soul is the essential part. The Person or Self just is a soul, and the soul is an essentially conscious and rational substance. To be conscious is to be aware of one’s own thoughts or ideas or to think about one’s own thoughts. To possess consciousness or the possibility of having consciousness are essential features of a soul. Something cannot qualify as a soul if it is not conscious and has no capacity to be conscious. Hence, it makes no sense to talk of persons in the absence of consciousness or capacity for it, nor does it make sense to talk of consciousness in the absence of any thoughts. This is the Platonic account of personhood defended most clearly in the Phaedo, which treats the soul as the only essential and enduring aspect of persons. But when one speaks of human persons one must of necessity also speak of a human body. A human person just is a person with a human body, and it makes no sense to talk of a human person separate from his body. To talk of a ‘disembodied human soul’ is best understood to signify the soul of someone who once possessed a human body. The Soul is a non-physical rational substance, because it is not physical it cannot be divided into parts. (Phaedo 78b-84b)

Another rival account of Selves is that they are merely collections of thoughts, and no aggregate collection of thoughts is identical to another therefore no two persons are exactly identical. In other words, because each person has different thoughts, at one time or another, no two persons are identical and Selves are essentially composites of ιδέες. Simmias speaks of the body as Lyre and the Self as the melody produced by it. (Ph. 85e-86d) The Self is the aggregate collection of the musical notes which make up the melody and is not an indivisible unity.

In the Parmenides, these two rival explanations of identity are put in sharp contrast and hypotheses are given which may harmonize them. (Parmenides 129b, 129c) The dialogue depicts Socrates as a young novice and Parmenides as the aged philosopher who has carefully meditated on these issues. (Par. 128d, 128e) This is a sharp contrast with most of the other Platonic dialogues where Socrates is put in the place of the wise elder. The primary concern of Socrates and Parmenides is with the Self and how it may participate in any particular ιδέα in the world of forms. The concern is not so much with rocks, or other non-rational things, because they cannot intellectualize any particular ιδέα, this point is made clear by Socrates who asks “if anyone could show in the abstract ideas, which are intellectual conceptions, this same multifarious and perplexing entanglement which you described in visible objects.” (Par. 129e, 130a) The argument which follows is primarily (though not exclusively) about the intellectual conceptions of abstract objects, not their instantiations in visible objects. Socrates summarizes the central problem this way, 

“I have often been in doubt, O Parmenides, regarding whether it is necessary to speak of Selves (αυτών) just as we did about those ideas or in another manner.” 

ἐν ἀπορίᾳ, φάναι, πολλάκις δή, ὦ Παρμενίδη, περὶ αὐτῶν γέγονα, πότερα χρὴ φάναι ὥσπερ περὶ ἐκείνων ἢ ἄλλως. (130c)

The argument implicit in these considerations is what has sometimes come to be known as the “Modal Argument” for dualism. It might be summarized this way. It is possible for minds to exist without physical bodies, and any physical object can be divided into parts. (One might divide a desk into constituent drawers or legs, etc. or as Zeno’s paradox Achilles and the tortoise demonstrates, it is always possible to divide any finite length in half infinitely many times.) But it is not possible to divide a mind into parts, it makes no sense to speak of “half a mind,” or “a quarter of a mind”—something is either conscious or it is not, and this is a sharp distinction. Therefore, since minds cannot be divided into parts they are not physical. But since there is a perception of composition with the ideas or forms, minds cannot be reduced to collections of ideas. Minds must be indivisible and simple substances. But how is this to be reconciled with the multiplicity of ideas?